Injection drug use is the predominant mode of HCV transmission in the United States and most injection drug users have HCV infection. In East Baltimore, 80-90% of IDUs are infected with hepatitis C, which can cause progressive hepatic fibrosis (cirrhosis) over 20 or more years, leading, in some patients, to end-stage liver disease, hepatocellular carcinoma and death. Furthermore, coinfection with human immunodeficiency virus (HIV) is present in 30% of HCV-infected IDUs, and is associated with the more rapid progression of HCV-related liver disease. Treatment of hepatitis C with pegylated interferon/ribavirin (PEG/RBV) eradicates HCV infection in approximately one-half of patients. However, persons who use or have used injection drugs are typically excluded from these treatment protocols, as are persons with other comorbidities such as HIV infection and psychiatric disease. This research aims to address the reality that the persons most affected by HCV infection are the least studied and the least treated, a disparity that becomes even more compelling as the success of HCV therapy increases. However, the implementation of HCV care is hindered by the paucity of data regarding which HIV-infected and uninfected IDUs are eligible and need HCV treatment. To address these issue we propose to accomplish the following aims: 1) to determine proportion of HIV-infected and uninfected IDUs who are eligible for HCV therapy with PEG/RBV according to absolute and relative criteria; 2) To determine the medical necessity of HCV treatment among HIV-infected and uninfected persons who are eligible for the PEG/RBV (determined by liver histology and non-invasive markers); and 3) Given the experience of the investigative team and the extensive preliminary research, we anticipate providing data that will have important impact on the medical care HCV-infected IDUs with and without HIV coinfection as well as the development of policies for the management and delivery of hepatitis C care among IDUs.